Superconductor materials have long been known and understood by the technical community. Low-temperature (low-Tc) superconductors exhibiting superconductive properties at temperatures requiring use of liquid helium (4.2° K), have been known since about 1911. However, it was not until somewhat recently that oxide-based high-temperature (high-Tc) superconductors have been discovered. Around 1986, a first high-temperature superconductor (HTS), having superconductive properties at a temperature above that of liquid nitrogen (77° K) was discovered, namely YBa2Cu3O7−x (YBCO), followed by development of additional materials over the past 15 years, including Bi2Sr2Ca2Cu3O10+y (BSCCO), and others. The development of high-Tc superconductors has brought potentially, economically feasible development of superconductors with liquid nitrogen, rather than the comparatively more expensive cryogenic infrastructure based on liquid helium.
Of the myriad of potential applications, the industry has sought to develop use of such materials in the power industry, including applications for power generation, transmission, distribution, and storage. In this regard, it is estimated that the native resistance of copper-based commercial power components is responsible for quite significant losses in electricity, and accordingly, the power industry stands to gain significant efficiencies based upon utilization of high-temperature superconductors in power components such as transmission and distribution power cables, generators, transformers, and fault current interrupters. In addition, other benefits of high-temperature superconductors in the power industry include an increase in one or two orders of magnitude of power-handling capacity, significant reduction in the size (i.e., footprint) of electric power equipment, reduced environmental impact, greater safety, and increased capacity over conventional technology. While such potential benefits of high-temperature superconductors remain quite compelling, numerous technical challenges continue to exist in the production and commercialization of high-temperature superconductors on a large scale.
Among the many challenges associated with the commercialization of high temperature superconductors, there remains the technical challenge in the power industry of fabricating HTS cables and devices in such a way that they operate with negligible alternating current (ac) losses. AC current is the dominant form in most of the world's power cable-based devices, and ac applications of HTS tapes operate with non-negligible energy losses, with the energy escaping in the form of heat. This impacts the efficiency of the system beyond mere energy loss since the heat generated must be removed from the environment of the device.
Superconductors operate in the temperature range of 4°-85° K, far below ambient temperature (298° K). Thus, superconductors require refrigeration, and refrigeration requires continuous expenditure of energy, for example, if the heat caused by the electrical current flowing in superconductor wires is at 77° K and is dissipated at the rate of 1 Watt, then refrigerators must be supplied with approximately 10-40 Watts of electrical power to dissipate that generated heat. Absent this refrigeration, the superconductor would warm itself to above its superconducting temperature and cease to operate as a superconductor, thereby eliminating any advantage and, in particular, providing worse performance than conventional copper conductors.
The heat generated must be eliminated to cost-effectively maintain low temperatures required by the superconductor. A successful solution to this problem would reduce operating costs by reducing the added cooling energy needed. One significant problem with HTS tapes is that unwanted ac magnetic fields are generated by the current flowing in the neighboring HTS tapes which causes ac losses. Because the HTS tape material and geometry is anisotropic, magnetic fields passing perpendicular to the preferred direction generates significantly greater losses than those of parallel fields.
In view of the foregoing, there exists a need for improved superconductors, and in particular, in the provision of commercially viable superconducting tapes, as well as methods for forming the same, and power components utilizing such superconductor tapes.